The present invention relates to an air-tightly sealable container with a bell jar covering provided with a sealing mechanism between the bell jar covering and the base plate on which the bell jar covering is mounted to be used for storage and transportation of various precision products to be kept absolutely free from contamination with atmospheric dust particles such as semiconductor silicon wafers.
The routine delivery system of semiconductor silicon wafers is that the silicon wafers as produced in the plant of a wafer producer are packaged in a specially designed container for transportation and transported therein to the plant of a manufacturer of semiconductor devices such as integrated circuits. Similar containers are used also within the plant of the device manufacturers for the purpose of inhouse transfer of intermediate products from a line to a subsequent line for the next step of working.
Needless to say, a semiconductor silicon wafer is a product of extremely high purity and must be kept away from any trace contamination, on the base of which ultrafine and extremely delicate electronic circuits are to be built so that the container therefor must be provided with a very reliable sealing mechanism by means of which intrusion of any trace amount of particulate foreign matters such as dust particles can be completely prevented.
One of the most traditional and simple way to obtain an air-tight sealing condition of the opening in such a container is that a pressure-sensitive adhesive tape is attached along the seam line of the container body and the covering all around or an elastic gasket member is interposed between the open periphery of the container body and the periphery of the covering under an appropriate compression so as to eliminate any smallest interstices or gaps, otherwise through which intrusion of dust particles may take place, to ensure a hermetic sealing condition.
These conventional methods for sealing are each not free from difficult problems. For example, adhesion of the pressure-sensitive adhesive tape to the surface of the container is sometimes not perfect due to occurrence of creases or twists of the tape depending on the outer configuration of the container and the worker's skill so that the hermetic sealing condition by this means is not always very reliable unless an unduly long time is taken for the taping works if not to mention possible contamination of the outer surface of the container with the adhesive. In addition, such a taping work is hardly susceptible to automatization.
The sealing method by using a rubber gasket also requires a clamping mechanism by which the container body and the covering are engaged and fastened each to the other and an appropriate compressive force is applied to the elastic gasket member.
In the current trend toward full automation of various production lines, it is eagerly desired to develop an air-tight sealing mechanism of a container with a bell jar covering which can be operated by an automatic machine for closing and opening the container.